This invention relates to an oscillating member for transforming a rotary motion into a reciprocating motion, which member is connected by a film hinge to a stationary member and comprises a resiliently flexible oscillating arm, which has in its free end portion a bearing bore for a crankpin of a shaft of a drive motor.
An oscillating member of this kind is known from Opened German Specification No. 2,117,319 and constitutes part of an oscillating frame, which serves to drive the movable shear blade of hair clippers and can be described in simplified form as a four-bar linkage having parallel sides and parallel ends and having film hinges rather than pivot joints. Film hinges are resiliently flexible strips or elastic bars having portions which are smaller in cross-section and can be resiliently bent from a position of rest about an axis which is parallel to their transverse axis. Owing to the kinematics of a four-bar linkage, the known oscillating frame has the disadvantage that the oscillating bar which carries the shear blade cannot only oscillate in the plane of the four-bar linkage but in accordance with the arcs of circles described by the end points of the film hinges describes in that plane a translational motion which is superposed on the reciprocating motion. This translational up and down motion at right angles to the reciprocating motion of the oscillating bar, which is pivotally movable parallel to itself, can be tolerated in hair clippers, where such translational motion will result merely in a slight gyratory motion of the movable shear blade on the fixed shear blade. But there are numerous machines and apparatus which must be operated to perform a straight-line reciprocating motion that is derived from a rotary motion produced by a drive motor.
An oscillating frame for deriving a straightline reciprocating motion from a rotary motion produced by a drive motor has been described in the prior German Patent Application No. P 29 1o 469. In that known oscillating frame, the oscillating bar that is connected to the element to be driven performs a reciprocating translational motion at right angles to the drive shaft of the drive motor. On the other hand, numerous advantageous devices could be made if they could be driven by a reciprocating translational motion which is derived from the rotation of the drive motor and aligned with the axis of rotation of the motor.